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Search for long-lived particles at ATLAS

Search for long-lived particles at ATLAS. Osamu JINNOUCHI (KEK) on behalf of ATLAS SUSY (exotic) group Supersymmetry in 2010’s at Hokkaido-university June 21, 2007. Long-lived particles search in ATLAS.

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Search for long-lived particles at ATLAS

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  1. Search for long-lived particles at ATLAS Osamu JINNOUCHI (KEK) on behalf of ATLAS SUSY (exotic) group Supersymmetry in 2010’sat Hokkaido-university June 21, 2007

  2. Long-lived particles search in ATLAS • Long-lived particles search (long enough to pass through detector) and their discovery --would directly address many important open questions to particle physics • Dark matter in the universe • Hierarchy problem • Extra dimension • flavor question • charge quantization • ... etc • If such particles produced at LHC, Can we(=ATLAS) effectively detect them ? It is important to know and develop the detection ability of ATLAS for such particles JINNOUCHI (KEK), SUSY 2010's

  3. outline • Introduction • sensible detectorsin ATLAS for the search • trigger issues • reconstruction of long-lived particles • summary JINNOUCHI (KEK), SUSY 2010's

  4. long-lived particles in the context of SUSY scenarios many candidates on the market (already many in SUSY scenarios only!) GMSB NLSP decays to LSP only via the gravitational coupling, thus could be long-lived • Non-pointing Photons (decay on flight) • Penetrating Sleptons Split SUSY (in MSSM scenario) Squarks are heavy, suppressing Gluino decays hence Gluino could be long-lived • Colored heavy particle (R-hadrons) AMSB and are mass de-generate chargino could be long-lived (decay on flight : Kink track) long hep-ph/0611040 many possible different event topologies ATLAS could cover with multi-purpose detectors

  5. possible event topologies, detection strategies Regardless of the models, categorized by the event signatures • Such particles are generally produced in pairs 1) direct production (small s ) 2) cascade decay products (SUSY) • Decay length? • Charge (Electric? magnetic? color?)  different detector response heavy slow particles • (A) Sleptons, R-hadrons • (heavy slow particles) • large ionization energy loss • nuclear int. (R-hadron case) • delay (TOF) reconstructed in Muon chamber • (B) Long-lived neutralino • (Non-pointing photon) • decay vertex is somewhere in the inner tracker volume kink track (on plan!) (A) non-pointing photons mSugra like (B) detailed study using Geant4 full detector simulation is inevitable JINNOUCHI (KEK), SUSY 2010's

  6. 2. Detectors in ATLAS sensitive to the long-lived particle search JINNOUCHI (KEK), SUSY 2010's

  7. (A) interaction of heavy particles in ATLAS nuclear int. only for R-hadrons Electromagnetic interactions (Slepton, R-hadron) • Ionization losses dominate (~1/b2 in low b, nearly MIP at b~1) Nuclear interactions (R-hadron) • gluino = spectator (reservoir of kinetic energy) • interaction by p/r/K/p/n cloud low energy deposit = ~1GeV x 10-15 interactions • charge flipping (~12) implemented ATLAS Prelim. Energy loss per int. (GeV) Geant4 300 GeV/c2 gluino in iron R-hadron Energy (GeV) JINNOUCHI (KEK), SUSY 2010's

  8. (A) signature of heavy particles in ATLAS (1) • Inner detectors • slow penetrating heavy particles • TRT (transition radiation tracker) (36 hits/track) -- good for dE/dx • heavily ionizing ==> can mimic TR • different behavior against muons • low-Pt end heavy particles Ionization • Higt-Pt end muons  TR • Calorimeters • similar longitudinal profile as muons • (R-hadrons) energy deposit - large fluctuation due to nuclear interactions ATLAS Prelim. m g 300GeV/c2 ~ JINNOUCHI (KEK), SUSY 2010's

  9. (A) signature of heavy particles in ATLAS (2) • Muon detectors • muon spectrometer systems for TOF (b) meas. At Level-2 trigger stage, quick calculation available with • RPC(barrel) 3.125ns resolution In Offline, more time/cpu consuming but precise • MDT(barrel + end cap) ~0.7ns resolution • tracking reco assumes b=1 • track fit c2 better for optimized t0 MDT drift time optimization JINNOUCHI (KEK), SUSY 2010's

  10. (B) detection of non-projecting photons • ATLAS ECal reconstruct the h in pointing geometry (from barycenter of the each layer) • good incident angle sensitivity in h, much less sensitivity in f Front layer Readout electrode =0 Middle layer =0.8 Back layer =1.4 Pre-sampler granularity (Dh x Df) r EM shower  60 GeV EM shower  60 GeV Middle Front ~ G ~ c 0 pointing non-pointing JINNOUCHI (KEK), SUSY 2010's

  11. 3. Trigger issues JINNOUCHI (KEK), SUSY 2010's

  12. (A) general issues of slow particles • large detector has advantage in TOF meas. with Muon system • timing is a critical issue with LHC BC (=25ns) [ LEP(25ms), Tevatron(396ns), HERA(96ns) ] • only b > 0.5 will be triggered in current BC • offline is fine, but reconstruction is not optimized 25ns Severer constraint for EndCap Atlas level-1 muon trigger system RPC (Barrel subsystem) and TGC (Endcap subsystem) RPC r = 6.8, 7.5 and 10m TGC z = 12.9, 14, 14.5m JINNOUCHI (KEK), SUSY 2010's

  13. (A) trigger for slow heavy particles (sleptons) • main source of background is inclusive muons • development of physics trigger menu for stau is on-going • (LVL2 trigger) can measure b(=v/c) with RPC TOF (3.1ns resolution) • mass reconstruction is possible at LVL2 (from b, p) • pre-selection of ‘slepton like’ events possible even at the LVL-2 pT>40GeV M>40GeV b<0.97 < 2Hz at 1034cm-2s-1 muon slepton bm 1nb at pT=40GeV ATLAS Prelim. pTm [GeV] inclusive single muon xsection L2 mass [GeV] JINNOUCHI (KEK), SUSY 2010's

  14. (B) trigger for non-pointing photons • event topology much looks like a general SUSY signature • will use ordinary SUSY trigger menu i.e. EtMiss + Jets • feasibility to use the standard photon menu, or its extension is currently under investigation ATLAS Std. photon trigger menu jet g missing ~ ~ ATLAS Prelim. G G trigger (EF) efficiency w.r.t. non-point MC photon (leading pT>60GeV) m missing g ID CAL jet jet e dh = h(point) – h(geom) JINNOUCHI (KEK), SUSY 2010's

  15. 4. Offline reconstruction of the long-lived particles JINNOUCHI (KEK), SUSY 2010's

  16. (A) Reconstruction of the R-hadrons Charge flip ID  Muon [charge flipping] • charge flipping reproduces int. models [mass determination] • average b obtained for momentum intervals • from the b vs. p correlation  mass • Mass scale determined to O(5-10%) + initial charge - initial charge ATLAS Prelim. doubly charged ATLAS Prelim. ATLAS Prelim. • mean = 306GeV • = +/- 16GeV • (input: 300GeV) MDT hits>10 |h |<2.5 b JINNOUCHI (KEK), SUSY 2010's

  17. (A) Reconstruction of the sleptons • Sleptons are reconstructed as muons • in the current software configuration, lower b (<0.5) lost due to the f info taken from RPC/TGC (using current BC) • inefficiency at 0.5<b<0.8, due to the bad reconstruction c2 from assuming b=1 • development of offline muon software is on-going, b measurement O(5-10%) • the plan to recover the next bunch crossing is on discussions ATLAS Prelim. efficiency reconstruction (b=1 assumed) ID loose (fit c2/ndof < 5 maching c2<20) ID tight (fit c2/ndof<2 matching c2<10) hep-ph/0010081 mt =100.1GeV ATLAS Prelim. m = pmeas/bgmeas 5% 15% offline b reconstruction bmeas JINNOUCHI (KEK), SUSY 2010's

  18. (B) Reconstruction of non-pointing photons • global goal of the non-pointing photon is • the ‘observation’ • the ‘decay length’ measurements which directly connects to SUSY scale • efficiency, resolution in terms of “degree of non-pointing” ATLAS Prelim. dh = h(point) – h(geom) Incident angle dependence ATLAS Prelim. Rec resol. < 0.002 Rec dh (Rec -- Truth) Efficiency Efficiency Rec+ID Rec+ID ATLAS Prelim. 1m 2m decay vertex distance from IP(0,0,0) dh = h(point) – h(geom) JINNOUCHI (KEK), SUSY 2010's

  19. (B) Reconstruction of the non-pointing photons • with g only, decay vertex cannot be reconstructed • instead looking at inter section z’ • reconstruction is ok, std photon ID has strong dependence • the work on-going for ‘non-pointing ID’ : save the non-pointing while keep the bkg rejection • usage of LAr timing, photon conversion is a next plan EM shower  60 GeV beam axis 0 z’ ATLAS Prelim. MC pT>60GeV Reconstruction Barrel only ATLAS Prelim. ~ G std. IDs (tight/loose) recovery of ID-efficiency (removing h width cut on 2nd layer) ~ c Z’ distribution (cm) JINNOUCHI (KEK), SUSY 2010's

  20. Summary • heavy long-lived particles are predicted in many models • ATLAS is equipped with multiple detector components sensitive to such particle searches • full detector simulations to describe the interactions and decays of these particles are ready • the customized menu for triggers, optimized offline particle reconstructions are being studied and still are developing -- tuned for the early discovery Let’s fully prepared for the real data and see what ATLAS will show us from 2008 JINNOUCHI (KEK), SUSY 2010's

  21. reference • [p4] hep-ph/0611040, M. Fairbairn et al. • [p7] MoriondQCD05, A. C. Kraan QCHS-06, R. Mackeprang • [p8] ATLAS SUSY WG, Apr 07, R. Mackeprang • [p9] ATLAS SUSY WG, Sept 04, A. C. Kraan • [p13] ATAS SUSY WG, June 07, H.Nomoto et al. • [p16] flip, mass • [p17] ATAS SUSY WG, June 07, H. Nomoto et al. hep-ph/0010081 S. Ambrosanio et al. • [p18] ATAS SUSY WG, Sept 07, O. Jinnouchi • [p19] ATAS EG WG, June 07, H. Heywood JINNOUCHI (KEK), SUSY 2010's

  22. BACKUP SLIDES JINNOUCHI (KEK), SUSY 2010's

  23. (A) trigger for slow heavy particles (slepton, R-hadron) The fate of the hadron-colliderexp. Data cannot be analyzed unless it is triggered ! • Heavy penetrating particles are triggered as muons, generally produced in pairs • inclusive high-pT single muon menu • must reach the last trigger stations in time for coincidence • if faster one triggers in right bunch crossing, the other can be reconstructed in offline GMSB Slepton M=100GeV b spectrum GMSB Slepton M=100GeV number of Muon trigger candidates (b, acceptance) JINNOUCHI (KEK), SUSY 2010's

  24. JINNOUCHI (KEK), SUSY 2010's

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